Usually, power semiconductor devices are mounted onto large heat sinks with or without extra cooling measures, such as fan cooling or fluid cooling. Power semiconductor devices are semiconductor devices used as switches or rectifiers in power electronic circuits. Examples are power diodes, Thyristors, IGBTs (insulated gate bipolar transistors) and power MOSFETs.
Heat sinks with or without extra cooling measures are designed in such a manner that in case of full power demand the temperature of the power semiconductor device remains below the absolute maximum as defined by its specifications. When the power demand is lowered or stopped, the cooling system keeps on transferring heat in the same rate as for full power, causing the temperature of the complete cooling system, i.e. the heat sink and the components mounted to it, to decrease very rapidly. When the power demand is increased again, the temperature will also rise another time.
If the power semiconductor device is repetitively used at maximum power alternated with short time intervals in which no or only low power is needed, the temperature of the power semiconductor device will vary between the periods of full power demand in which the temperature will rise to its maximum and the periods of low or no power demand, in which the device temperature will decrease rapidly due to the cooling capacity of the implemented heat sink and, if available, cooling system. In this way, the device temperature will possibly experience large temperature variations.
For example U.S. Pat. No. 6,116,040 does disclose an apparatus for cooling of electronics of a variable frequency drive associated with a refrigerant compressor. By means of the compressor drive, the temperature of the power electronics is maintained in a desired temperature range.
The lifetime of semiconductor devices is determined by several processes which each lead to a deterioration of the intended device characteristics over time up to the complete failure of the device. For power semiconductors, one of the most important processes is mechanical stress due to thermal cycling. Due to the finite thermal resistance between the semiconductor die and the base upon which it is mounted and the differences in the thermal expansion coefficients of the materials involved, changes in power dissipation over time inevitably lead to thermal stresses. These stresses can lead to material fatigue, manifesting itself in rupture of bond wires and/or degradation of the soldering connection between the die and the base upon which it is mounted.
Rupture of bond wire can either lead to direct device failure or to further increased stress to other bond wires in the case that multiple bond wires are connected in parallel, as it is often the case in power semiconductor modules.
As a consequence, if power semiconductor devices are repetitively used at maximum power alternated with intervals of time in which no or low power is needed, the temperature of such power devices even when mounted on large heat sinks with or without extra cooling measures will vary greatly between the periods of full power demand. As a consequence, the die temperature will experience large temperature variations which will reduce the lifetime of the power semiconductor device.
U.S. Pat. No. 5,569,650 relates to an electronic chip cooling device and more particularly to a device which provides active cooling to reduce temperature excursions of electronic chips, which will limit thermal fatigue, increase product lifecycle, allow for larger chips and permit chips to be directly attached to substrates with unmatched coefficients of thermal expansion with less reliability concerns. In an embodiment, an electronic chip is attached to the substrate and a thermal electric cooling device is secured to the exposed surface of the chip. A temperature sensing means such as a thin film thermal couple is attached between the cold side of the thermal electric cooling (TEC) device and the chip. The temperature sensing means may alternative be built into the chip or the electronic package adjacent to the interconnection between the TEC device and the chip. Further, a heat sink is provided which is secured to the hot side of the TEC device. An output of the thermal couple is coupled to a feedback control circuit.
WO 2005/043618 A does disclose a method and arrangement in connection with an inverter that comprises several power semiconductor components and a control apparatus arranged to control them, the control apparatus being arranged to control the power semiconductor components in response to a control quantity to generate an output voltage.
US 2005/039465 A1 does disclose a cooling system for audio equipment which uses a temperature sensor and a Peltier effect module in a feedback control loop. The cooling system reads the temperature sensor to obtain the temperature of an audio component of the equipment and adjusts the drive for the Peltier effect module that cools the audio component to prevent overheating of the component.
DE 10233836 A1 does disclose an electronic control unit comprising a housing which comprises various electronic components, wherein the electronic components are required to be driven below a maximum temperature. For cooling the electronic components a Peltier element is provided.